Downlink channel parameters determination for a multiple-input-multiple-output (MIMO) system

ABSTRACT

Embodiments of methods and apparatus for providing downlink channel parameters determination for downlink channels associated with a multiple-input-multiple-output (MIMO) system are generally described herein. Other embodiments may be described and claimed.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 13/543,371, filed Jul. 6, 2012, entitled “Downlink ChannelParameters Determination For A Multiple-Input-Multiple-Output (Mimo)System,” which is a continuation of U.S. patent application Ser. No.12/882,957, filed Sep. 15, 2010, entitled “Downlink Channel ParametersDetermination For A Multiple-Input-Multiple-Output (Mimo) System,” whichis a continuation of U.S. patent application Ser. No. 11/617,313, filedDec. 28, 2006, entitled “Downlink Channel Parameters Determination For AMultiple-Input-Multiple-Output (MIMO) System,” which claims priority toU.S. Patent Application No. 60/797,042, filed May 1, 2006, entitled“Methods and Apparatus for Providing A Power Loading and ModulationSelection System Associated with A Multiple-Input-Multiple-Output (MIMO)System,” and to U.S. Patent Application No. 60/784,418, filed Mar. 20,2006, entitled “System, Apparatus, Associated Methods and Protocols toSupport Next Generation Wireless Communications,” the entire disclosuresof which are hereby incorporated by reference in their entireties forall purposes, except for those sections, if any, that are inconsistentwith this specification.

TECHNICAL FIELD

The present disclosure relates generally to wireless communicationsystems, and more particularly, to methods and apparatus for providingdownlink channel parameters, such as bit or power loading and modulationor coding scheme selection for downlink channels in amultiple-input-multiple-output system.

BACKGROUND

As wireless communication becomes more and more popular at offices,homes, schools, etc., different wireless technologies and applicationsmay work in tandem to meet the demand for computing and communicationsat anytime and/or anywhere. For example, a variety of wirelesscommunication networks may co-exist to provide a wireless environmentwith more computing and/or communication capability, greater mobility,and/or eventually seamless roaming.

In particular, wireless personal area networks (WPANs) may offer fast,short-distance connectivity within a relatively small space such as anoffice workspace or a room within a home. Wireless local area networks(WLANs) may provide broader range than WPANs within office buildings,homes, schools, etc. Wireless metropolitan area networks (WMANs) maycover a greater distance than WLANs by connecting, for example,buildings to one another over a broader geographic area. Wireless widearea networks (WWANs) may provide the broadest range as such networksare widely deployed in cellular infrastructure. Although each of theabove-mentioned wireless communication networks may support differentusages, co-existence among these networks may provide a more robustenvironment with anytime and anywhere connectivity.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will be readily understood by thefollowing detailed description in conjunction with the accompanyingdrawings. To facilitate this description, like reference numeralsdesignate like structural elements. Embodiments of the invention areillustrated by way of example and not by way of limitation in thefigures of the accompanying drawings.

FIG. 1 is a schematic diagram representation of an example wirelesscommunication system according to an embodiment of the methods andapparatus disclosed herein;

FIG. 2 is a block diagram representation of an examplemultiple-input-multiple-output (MIMO) system of the example wirelesscommunication system of FIG. 1;

FIG. 3 is a block diagram representation of an example base station ofthe example MIMO system of FIG. 2;

FIG. 4 depicts an example chart associated with throughput;

FIG. 5 depicts another example chart associated with throughput;

FIG. 6 depicts an example chart associated with probability densityfunctions (PDFs);

FIG. 7 depicts yet another example chart associated with throughput;

FIG. 8 is a flow diagram representation of one manner in which theexample base station of FIG. 3 may be configured; and

FIG. 9 is a block diagram representation of an example processor systemthat may be used to implement the example base station of FIG. 3.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof wherein like numeralsdesignate like parts throughout, and in which is shown by way ofillustration embodiments in which the invention may be practiced. It isto be understood that other embodiments may be utilized and structuralor logical changes may be made without departing from the scope of thepresent invention. Therefore, the following detailed description is notto be taken in a limiting sense, and the scope of embodiments inaccordance with the present invention is defined by the appended claimsand their equivalents.

Various operations may be described as multiple discrete operations inturn, in a manner that may be helpful in understanding embodiments ofthe present invention; however, the order of description should not beconstrued to imply that these operations are order dependent.

For the purposes of the present invention, the phrase “A/B” means A orB. For the purposes of the present invention, the phrase “A and/or B”means “(A), (B), or (A and B)”. For the purposes of the presentinvention, the phrase “at least one of A, B, and C” means “(A), (B),(C), (A and B), (A and C), (B and C), or (A, B and C)”. For the purposesof the present invention, the phrase “(A)B” means “(B) or (AB)” that is,A is an optional element.

The description may use the phrases “in an embodiment,” or “inembodiments,” which may each refer to one or more of the same ordifferent embodiments. Furthermore, the terms “comprising,” “including,”“having,” and the like, as used with respect to embodiments of thepresent invention, are synonymous.

Embodiments of the present invention provide power loading andmodulation selection systems and methods for amultiple-input-multiple-output (MIMO) system.

Referring to FIG. 1, an example wireless communication system 100, inaccordance with various embodiments of the present invention, mayinclude one or more wireless communication networks, generally shown as110, 120, and 130. In particular, the wireless communication system 100may include a wireless personal area network (WPAN) 110, a wirelesslocal area network (WLAN) 120, and a wireless metropolitan area network(WMAN) 130. Although FIG. 1 depicts three wireless communicationnetworks, the wireless communication system 100 may include additionalor fewer wireless communication networks. For example, the wirelesscommunication networks 100 may include additional WPANs, WLANs, and/orWMANs. The methods and apparatus described herein are not limited inthis regard.

The wireless communication system 100 may also include one or moresubscriber stations, generally shown as 140, 142, 144, 146, and 148. Forexample, the subscriber stations 140, 142, 144, 146, and 148 may includewireless electronic devices such as a desktop computer, a laptopcomputer, a handheld computer, a tablet computer, a cellular telephone,a pager, an audio and/or video player (e.g., an MP3 player or a DVDplayer), a gaming device, a video camera, a digital camera, a navigationdevice (e.g., a GPS device), a wireless peripheral (e.g., a printer, ascanner, a headset, a keyboard, a mouse, etc.), a medical device (e.g.,a heart rate monitor, a blood pressure monitor, etc.), and/or othersuitable fixed, portable, or mobile electronic devices. Although FIG. 1depicts five subscriber stations, the wireless communication system 100may include more or less subscriber stations.

The subscriber stations 140, 142, 144, 146, and 148 may use a variety ofmodulation techniques such as spread spectrum modulation (e.g., directsequence code division multiple access (DS-CDMA) and/or frequencyhopping code division multiple access (FH-CDMA)), time-divisionmultiplexing (TDM) modulation, frequency-division multiplexing (FDM)modulation, orthogonal frequency-division multiplexing (OFDM)modulation, multi-carrier modulation (MDM), and/or other suitablemodulation techniques to communicate via wireless links. In one example,the laptop computer 140 may operate in accordance with suitable wirelesscommunication protocols that require very low power such as Bluetooth®,ultra-wide band (UWB), and/or radio frequency identification (RFID) toimplement the WPAN 110. In particular, the laptop computer 140 maycommunicate with devices associated with the WPAN 110 such as the videocamera 142 and/or the printer 144 via wireless links.

In another example, the laptop computer 140 may use direct sequencespread spectrum (DSSS) modulation and/or frequency hopping spreadspectrum (FHSS) modulation to implement the WLAN 120 (e.g., the 802.11family of standards developed by the Institute of Electrical andElectronic Engineers (IEEE) and/or variations and evolutions of thesestandards). For example, the laptop computer 140 may communicate withdevices associated with the WLAN 120 such as the printer 144, thehandheld computer 146 and/or the smart phone 148 via wireless links. Thelaptop computer 140 may also communicate with an access point (AP) 150via a wireless link. The AP 150 may be operatively coupled to a router152 as described in further detail below. Alternatively, the AP 150 andthe router 152 may be integrated into a single device (e.g., a wirelessrouter).

The laptop computer 140 may use OFDM modulation to transmit largeamounts of digital data by splitting a radio frequency signal intomultiple small sub-signals, which in turn, are transmittedsimultaneously at different frequencies. In particular, the laptopcomputer 140 may use OFDM modulation to implement the WMAN 130. Forexample, the laptop computer 140 may operate in accordance with the802.16 family of standards developed by IEEE to provide for fixed,portable, and/or mobile broadband wireless access (BWA) networks (e.g.,the IEEE std. 802.16-2004 (published Sep. 18, 2004), the IEEE std.802.16e (published Feb. 28, 2006), the IEEE std. 802.16f (published Dec.1, 2005), etc.) to communicate with base stations, generally shown as160, 162, and 164, via wireless link(s).

Although some of the above examples are described above with respect tostandards developed by IEEE, the methods and apparatus disclosed hereinare readily applicable to many specifications and/or standards developedby other special interest groups and/or standard developmentorganizations (e.g., Wireless Fidelity (Wi-Fi) Alliance, WorldwideInteroperability for Microwave Access (WiMAX) Forum, Infrared DataAssociation (IrDA), Third Generation Partnership Project (3GPP), etc.).The methods and apparatus described herein are not limited in thisregard.

The WLAN 120 and WMAN 130 may be operatively coupled to a common publicor private network 170 such as the Internet, a telephone network (e.g.,public switched telephone network (PSTN)), a local area network (LAN), acable network, and/or another wireless network via connection to anEthernet, a digital subscriber line (DSL), a telephone line, a coaxialcable, and/or any wireless connection, etc. In one example, the WLAN 120may be operatively coupled to the common public or private network 170via the AP 150 and/or the router 152. In another example, the WMAN 130may be operatively coupled to the common public or private network 170via the base station(s) 160, 162, and/or 164.

The wireless communication system 100 may include other suitablewireless communication networks. For example, the wireless communicationsystem 100 may include a wireless wide area network (WWAN) (not shown).The laptop computer 140 may operate in accordance with other wirelesscommunication protocols to support a WWAN. In particular, these wirelesscommunication protocols may be based on analog, digital, and/ordual-mode communication system technologies such as Global System forMobile Communications (GSM) technology, Wideband Code Division MultipleAccess (WCDMA) technology, General Packet Radio Services (GPRS)technology, Enhanced Data GSM Environment (EDGE) technology, UniversalMobile Telecommunications System (UMTS) technology, Third GenerationPartnership Project (3GPP) technology, standards based on thesetechnologies, variations and evolutions of these standards, and/or othersuitable wireless communication standards. Although FIG. 1 depicts aWPAN, a WLAN, and a WMAN, the wireless communication system 100 mayinclude other combinations of WPANs, WLANs, WMANs, and/or WWANs. Themethods and apparatus described herein are not limited in this regard.

The wireless communication system 100 may include other WPAN, WLAN,WMAN, and/or WWAN devices (not shown) such as network interface devicesand peripherals (e.g., network interface cards (NICs)), access points(APs), redistribution points, end points, gateways, bridges, hubs, etc.to implement a cellular telephone system, a satellite system, a personalcommunication system (PCS), a two-way radio system, a one-way pagersystem, a two-way pager system, a personal computer (PC) system, apersonal data assistant (PDA) system, a personal computing accessory(PCA) system, and/or any other suitable communication system. Althoughcertain examples have been described above, the scope of coverage ofthis disclosure is not limited thereto.

Referring to FIG. 2, an example wireless MIMO system 200, in accordancewith various embodiments of the present invention, may include a basestation 210 and one or more subscriber stations, generally shown as 220and 225. The wireless MIMO system 200 may include a point-to-point MIMOsystem and/or a point-to-multiple point MIMO system. For example, apoint-to-point MIMO system may include the base station 210 and thesubscriber station 220. A point-to-multiple point MIMO system mayinclude the base station 210 and the subscriber station 225. The basestation 210 may transmit data streams to the subscriber stations 220,225 simultaneously. For example, the base station 310 may transmit twodata streams to the subscriber station 220 and one data stream to thesubscriber station 225. Although FIG. 2 may depict one subscriberstation, the wireless MIMO system 200 may include additional subscriberstations.

The base station 210 may transmit two or more data streams over fourtransmit antennas 250, generally shown as 252, 254, 256, and 258.Although FIG. 2 depicts four transmit antennas, the base station 210 mayinclude additional or fewer transmit antennas. The methods and apparatusdescribed herein are not limited in this regard.

In the example of FIG. 3, the base station 300 may include a networkinterface device (NID) 340, a processor 350, and a memory 360. The NID340, the processor 350, and the memory 360 may be operatively coupled toeach other via a bus 370. While FIG. 3 depicts components of the basestation 300 coupling to each other via the bus 370, these components maybe operatively coupled to each other via other suitable direct orindirect connections (e.g., a point-to-point connection or apoint-to-multiple point connection).

The NID 340 may include a receiver 342, a transmitter 344, and anantenna 346. The base station 300 may receive and/or transmit data viathe receiver 342 and the transmitter 344, respectively. The antenna 346may include one or more directional or omni-directional antennas such asdipole antennas, monopole antennas, patch antennas, loop antennas,microstrip antennas, and/or other types of antennas suitable fortransmission of radio frequency (RF) signals. Although FIG. 3 depicts asingle antenna, the base station 300 may include additional antennas.For example, the base station 300 may include a plurality of antennas toimplement a multiple-input-multiple-output (MIMO) system.

Although the components shown in FIG. 3 are depicted as separate blockswithin the base station 300, the functions performed by some of theseblocks may be integrated within a single semiconductor circuit or may beimplemented using two or more separate integrated circuits. For example,although the receiver 342 and the transmitter 344 are depicted asseparate blocks within the NID 340, the receiver 342 may be integratedinto the transmitter 344 (e.g., a transceiver). The methods andapparatus described herein are not limited in this regard.

In general, FIG. 4 depicts an example of throughput of a MIMO systemwith hybrid automatic repeat request (H-ARQ), in accordance with variousembodiments. Solid black curves are for open-loop. The other solidcurves are for closed-loop with adaptive bit loading (ABL). Dashedcurves are for closed-loop without adaptive bit loading, i.e. uniformbit loading (UBL). The numbers in the brackets is the number of bitsloaded on the stream per subcarrier.

In general, FIG. 5 depicts another example of throughput of a MIMOsystem with H-ARQ, in accordance with various embodiments. Solid curvesare for closed-loop with adaptive bit loading (ABL) and adaptive powerloading. Dashed curves are for closed-loop with adaptive bit loading,but without adaptive power loading. The numbers in the brackets is thenumber of bits loaded on the stream per subcarrier.

Adaptive bit loading and adaptive power loading (or power water filling)across beamformed spatial channels may improve the performance of MIMOsystems as shown in FIGS. 4 and 5. The bit and power loadings may bedetermined by the channel gains of the channels and the noise plusinterference level on each channel. In singular value decomposition(SVD) beamformed MIMO, the interference across spatial channels isgenerally mitigated and may be ignored. The thermal noise level may beestimated using the KTB equation (where K is Boltzman's constant, T istemperature in Kelvin and B is signal bandwidth in Hz) and noise figure,e.g. 1-5 dB. The gain of each channel (or equivalently signal to noiseplus interference ratio (SINR)) usually requires feedback. However, thefeedback channel is generally costly in WMAN. Thus, it is desirable toreduce the feedback overhead. In a time division duplex (TDD) system,the feedback channel is generally reciprocal between downlink anduplink. A base station may use the uplink traffic or channel training toestimate the downlink channel. This saves the channel feedback. However,the channel reciprocity doesn't exist for a frequency division duplex(FDD) system.

In general, FIG. 6 depicts PDFs of the singular values of MIMO channelmatrix with 4×1, 4×2, 4×3, and 4×4 antenna configurations for IEEE802.11 n model B LOS (Line Of Sight).

In accordance with various embodiments of the present invention,although the channel matrix of MIMO is generally random, the singularvalues of the channel matrix, i.e. the gains of the beamformed channels,generally have narrower probability density functions (PDFs) than thatof the channel matrix entry. The PDF gets narrower as the number ofantennas increases, as may be seen in FIG. 6. The narrower the PDF, themore easily the random variable may be estimated. The stronger singularvalue generally has a narrower PDF than that of the weaker singularvalue. The strong singular values usually correspond to usable spatialchannels. In other words, the singular values are easier to estimatethan the matrix entry and the gain of usable channel is easier toestimate than the unusable channel. Furthermore, the correlation betweenantennas also narrows the PDF of the singular value, and makes theestimation relatively easier. Because the channel statistics (e.g. powerlevel of channel matrix entry and antenna correlation) are the same orlikely to be the same for uplink and downlink, the base station may usethe mean of singular value in the uplink as the estimation of theinstantaneous singular value in the downlink. The mean may be computedover frequency and/or time. In accordance with various embodiments,after the channel gain of the beamformed channel is estimated, the basestation may select the usable channels to send data and may determinethe modulation and power level for the selected channel. The performanceof such a scheme, in accordance with various embodiments, is illustratedin FIGS. 4 and 5.

In accordance with various embodiments of the present invention, theestimation of noise plus interference level may be improved by theconventional channel quality (CQI) feedback. CQI feed back is commonlyused in 3G and WiMAX. The collection of channel samples, which are usedto estimate the mean, should follow the operation in the system. Inaccordance with various embodiments, when multi-user diversity isemployed in an orthogonal frequency division multiple access (OFDMA)system, a subscriber station sorts the channel quality across frequency(and time) and requests that a base station uses the best channels tosend data. For example, the whole frequency band is partitioned intochunks of contiguous subcarriers, and the subscriber station feeds backthe indexes for the best three chunks and their beamforming matrixes. Inaccordance with various embodiments, the base station may use some ofthe fed back chunks to send data. Since the fed back channel is sorted,the base station may also sort the uplink channels with the sameparameters, e.g. chunk size and the total bandwidth. The estimation maythen be conducted on the sorted channel samples. In sum, the collectionof the matrix samples in the base station from the uplink should be asclose as possible to the matrix finally used in the downlink. Thecollected matrix may be transposed before use. The transpose reflectsthe asymmetry between downlink and uplink channels.

In accordance with various embodiments of the present invention, theidea of using the uplink channel to estimate downlink channel parametersmay be extended for non-beamformed MIMO. For example, the per antennarate control (PARC) mode may not employ transmit beamforming, but it mayemploy bit (and power) loading on each transmit antenna. In aconventional PARC mode, it requires the subscriber station to feed backthe channel quality of each data stream or bit loading information foreach transmit antenna, where one transmit antenna sends one data stream.In a modified PARC mode, a data stream may be sent by a spatial channelformed by multiple transmit antennas. The demodulation scheme is usuallyminimum mean-square error (MMSE) plus successive cancellation. If thedemodulation scheme is known at the base station, the base station maycollect channel matrixes in the uplink with the same or similarstatistics as those used in the downlink for PARC, and it may estimatethe channel quality of each data stream seen at the receiver using thesame demodulation scheme. After the estimation is completed, the basestation may decide how many streams are used and what the modulation andcoding scheme for each stream should be. Although the estimation isgenerally not accurate, it still provides information about theinstantaneous, random downlink channel. This may reduce the feedbackoverhead needed from the subscriber station. For example, the subscriberstation may only need to provide differential information to refine theestimation using the mean.

In addition to PARC mode, the idea may be used by open loop modes, inaccordance with various embodiments. For example, the base station mayestimate the channel quality from the uplink to decide the number ofdata streams and modulation/coding scheme for the downlink. The numberof data streams is generally dependent on the antenna correlations andSINR of each stream. SINR is generally dependent on received signalpower (or path loss) and demodulation scheme. Once the demodulationscheme is known or estimated, the SINR may be estimated using the uplinkchannel samples. After the SINR is estimated, the number of usablestreams and the modulation, coding scheme, and power level of thestreams may be determined.

In addition to the mean of channel quality or singular value, otherstatistics such as, for example, variance may also be useful and may beestimated, in accordance with various embodiments. The information maybe used to set margin for the selected power and bit loading. Forexample, a base station may use a lower bit loading scheme on theselected channel than that computed from the mean because the varianceis large and the estimation is not reliable. There may be multiple waysto compute the mean, e.g.

${\overset{\_}{x} = {\frac{1}{N}{\sum\limits_{i = 1}^{N}\;{x_{i}}}}},{or}$$\overset{\_}{x} = {\sqrt{\frac{1}{N}{\sum\limits_{i = 1}^{N}\;{x_{i}}^{2}}}.}$

Once the number of usable channels K is estimated, the base station maydynamically ask a subscriber station to feed back information (such asbeamforming matrix or SINR) only for the strongest K channels instead ofall channels, in accordance with various embodiments of the presentinvention. This generally reduces the feedback overhead of (closed-loop)MIMO. In addition, putting transmission power in the strongest fewchannels instead of all channels may significantly improve performancein low SNR region. This may be seen in FIG. 7. Therefore, the selectionof the channel number is an important application of the estimation byitself.

In accordance with various embodiments, the estimation from the uplinkfor the subscriber stations may also help the base station to schedulethe downlink transmission. For example, the base station may picksubscriber stations with good channel quality to serve first and waitfor the poor ones to change to be good (e.g. move out from a shadowfading). This type of scheduling is generally referred to as multiuserdiversity. The uplink estimation may facilitate multiuser diversityscheduling.

In general, FIG. 7 illustrates rank control that determines the numberof usable channels, in accordance with various embodiments. The curvesin legend 1 and 3 have the same maximum throughput while they use twoand three channels respectively. Legend 1 performs better than legend 3.Similarly, legend 2 outperforms legend 4.

Exemplary pseudo code, in accordance with various embodiments of thepresent invention, may be as follows:

1. Base station collects uplink channels according the mode used in thedownlink. The collected channels are transposed and treated as channelscollected from the downlink;

2. Compute the mean and variance of the channel quality for each spatialchannel or data stream;

3. Determine the number of usable streams or spatial channels, bitloading, power loading, and coding scheme on the usable channels orstreams jointly;

4. Select subscriber station(s) to which to transmit; and

5. Conduct downlink transmission using determined parameters.

At a subscriber station, it generally needs to know the power of eachpower loaded channel for demodulation, in accordance with variousembodiments. The base station may signal the power loading to asubscriber station using channel training symbols. The training symbolsmay be dedicated to the user in OFDMA system. Because the loadinggenerally is on the dedicated pilots, it doesn't affect the channelestimation of other users. The dedicated pilot may be sent over thebeamformed spatial channel. In addition to dedicated pilot, the powerlevel may be specified in a control channel or a broadcast channel sothat the receiver knows about the power level difference between thepower loaded data symbol and the channel training symbols (e.g. pilots)that are not power loaded.

In accordance with various embodiments of the present invention, FIG. 8depicts one manner in which base station 300 may be configured toprovide a power loading and modulation selection system. The exampleprocess 800 of FIG. 8 may be implemented as machine-accessibleinstructions utilizing any of many different programming codes stored onany combination of machine-accessible media such as a volatile ornon-volatile memory or other mass storage device (e.g., a floppy disk, aCD, and a DVD). For example, the machine-accessible instructions may beembodied in a machine-accessible medium such as a programmable gatearray, an application specific integrated circuit (ASIC), an erasableprogrammable read only memory (EPROM), a read only memory (ROM), arandom access memory (RAM), a magnetic media, an optical media, and/orany other suitable type of medium.

Further, although a particular order of actions is illustrated in FIG.8, these actions may be performed in other temporal sequences. Again,the example process 800 is merely provided and described in conjunctionwith the system and apparatus of FIGS. 2 and 3 as an example of one wayto provide a power loading and modulation selection system.

In the example of FIG. 8, the process 800 may begin with base station300 (FIG. 3) collecting uplink channel information according to the modeused in the downlink (block 810). Based at least in part on thecollected uplink channel information, the base station 300 may computechannel quality information of each spatial channel and/or data stream(block 820). For example, the base station may compute the mean and/orthe variance of the channel quality for each spatial channel and/or datastream. The channel quality information may be computed by estimating ausable number of channels. Based at least in part on the channel qualityinformation, the base station 300 may determine one or more downlinkchannel parameters (block 830). Downlink channel parameters may includethe number of usable data streams, the number of usable spatialchannels, bit loading, power loading, coding scheme, and/or othersuitable parameters. The base station 300 may receive feedbackinformation only for a subset of relatively stronger channels of theestimated usable channels (block 835). The base station 300 may selectone or more subscriber stations to which to transmit (block 840) basedat least in part on one or more downlink channel parameters.Accordingly, the base station 300 may communicate with one or moresubscriber stations (e.g., the subscriber stations 220 and/or 225) basedon the downlink channel parameters (block 850). The methods andapparatus described herein are not limited in this regard.

In general, the methods and apparatus described herein may use uplinkchannel to estimate parameters in the downlink channel. It reduces thefeedback overhead for power and bit loading in MIMO system. The methodsand apparatus described herein are not limited in this regard.

Although the methods and apparatus described herein may be associatedwith the Third Generation Partnership Project (3GPP) for the Long TermEvolution (LTE), the methods and apparatus described herein may bereadily applicable with other suitable wireless technologies, protocols,and/or standards. The methods and apparatus described herein are notlimited in this regard.

FIG. 9 is a block diagram of an example processor system 2000 adapted toimplement methods and apparatus disclosed herein. The processor system2000 may be a desktop computer, a laptop computer, a handheld computer,a tablet computer, a PDA, a server, an Internet appliance, a basestation, an access point and/or any other type of computing device.

The processor system 2000 illustrated in FIG. 9 includes a chipset 2010,which includes a memory controller 2012 and an input/output (I/O)controller 2014. The chipset 2010 may provide memory and I/O managementfunctions as well as a plurality of general purpose and/or specialpurpose registers, timers, etc. that are accessible or used by aprocessor 2020. In various embodiments, I/O controller 2014 of chipset2010 may be endowed with all or portions of the teachings of the presentinvention described above. The processor 2020 may be implemented usingone or more processors, WLAN components, WMAN components, WWANcomponents, and/or other suitable processing components. For example,the processor 2020 may be implemented using one or more of the Intel®Pentium® technology, the Intel® Itanium® technology, the Intel®Centrino™ technology, the Intel® Xeon™ technology, and/or the Intel®XScale® technology. In the alternative, other processing technology maybe used to implement the processor 2020. The processor 2020 may includea cache 2022, which may be implemented using a first-level unified cache(L1), a second-level unified cache (L2), a third-level unified cache(L3), and/or any other suitable structures to store data.

The memory controller 2012 may perform functions that enable theprocessor 2020 to access and communicate with a main memory 2030including a volatile memory 2032 and a non-volatile memory 2034 via abus 2040. The volatile memory 2032 may be implemented by SynchronousDynamic Random Access Memory (SDRAM), Dynamic Random Access Memory(DRAM), RAMBUS Dynamic Random Access Memory (RDRAM), and/or any othertype of random access memory device. The non-volatile memory 2034 may beimplemented using flash memory, Read Only Memory (ROM), ElectricallyErasable Programmable Read Only Memory (EEPROM), and/or any otherdesired type of memory device.

The processor system 2000 may also include an interface circuit 2050that is coupled to the bus 2040. The interface circuit 2050 may beimplemented using any type of interface standard such as an Ethernetinterface, a universal serial bus (USB), a third generation input/outputinterface (3G10) interface, and/or any other suitable type of interface.In various embodiments, interface circuit 2050 may be endowed with allor portions of the teachings of the present invention described above.

One or more input devices 2060 may be connected to the interface circuit2050. The input device(s) 2060 permit an individual to enter data andcommands into the processor 2020. For example, the input device(s) 2060may be implemented by a keyboard, a mouse, a touch-sensitive display, atrack pad, a track ball, an isopoint, and/or a voice recognition system.

One or more output devices 2070 may also be connected to the interfacecircuit 2050. For example, the output device(s) 2070 may be implementedby display devices (e.g., a light emitting display (LED), a liquidcrystal display (LCD), a cathode ray tube (CRT) display, a printerand/or speakers). The interface circuit 2050 may include, among otherthings, a graphics driver card.

The processor system 2000 may also include one or more mass storagedevices 2080 to store software and data. Examples of such mass storagedevice(s) 2080 include floppy disks and drives, hard disk drives,compact disks and drives, and digital versatile disks (DVD) and drives.

The interface circuit 2050 may also include a communication device suchas a modem or a network interface card to facilitate exchange of datawith external computers via a network. The communication link betweenthe processor system 2000 and the network may be any type of networkconnection such as an Ethernet connection, a digital subscriber line(DSL), a telephone line, a cellular telephone system, a coaxial cable,etc.

Access to the input device(s) 2060, the output device(s) 2070, the massstorage device(s) 2080 and/or the network may be controlled by the I/Ocontroller 2014. In particular, the I/O controller 2014 may performfunctions that enable the processor 2020 to communicate with the inputdevice(s) 2060, the output device(s) 2070, the mass storage device(s)2080 and/or the network via the bus 2040 and the interface circuit 2050.

While the components shown in FIG. 9 are depicted as separate blockswithin the processor system 2000, the functions performed by some ofthese blocks may be integrated within a single semiconductor circuit ormay be implemented using two or more separate integrated circuits. Forexample, although the memory controller 2012 and the I/O controller 2014are depicted as separate blocks within the chipset 2010, the memorycontroller 2012 and the I/O controller 2014 may be integrated within asingle semiconductor circuit.

Although certain embodiments have been illustrated and described hereinfor purposes of description of the preferred embodiment, it will beappreciated by those of ordinary skill in the art that a wide variety ofalternate and/or equivalent embodiments or implementations calculated toachieve the same purposes may be substituted for the embodiments shownand described without departing from the scope of the present invention.Those with skill in the art will readily appreciate that embodiments inaccordance with the present invention may be implemented in a very widevariety of ways. This application is intended to cover any adaptationsor variations of the embodiments discussed herein. Therefore, it ismanifestly intended that embodiments in accordance with the presentinvention be limited only by the claims and the equivalents thereof.

What is claimed is:
 1. An apparatus to be employed in an eNodeB (eNB),the apparatus comprising: a transmitter to transmit, on one or moredownlink channels of a number of downlink channels, a downlink signal toa subscriber station using downlink parameters that are determined basedon received uplink channel quality information; and a receiver coupledwith the transmitter, the receiver to receive, from the subscriberstation, an uplink message including feedback information correspondingto the downlink signal, wherein the feedback information is only for asubset of channels of the number of downlink channels, and wherein thenumber of the subset of channels is less than the number of downlinkchannels.
 2. The apparatus of claim 1, wherein the subset of channels isa subset of relatively stronger channels of the number of downlinkchannels.
 3. The apparatus of claim 1, wherein the uplink channelquality information is based on channel quality of uplink spatialchannels and/or data streams.
 4. The apparatus of claim 3, wherein theuplink channel quality information includes a mean or a variance ofchannel quality for each of the spatial channels and/or data streams. 5.The apparatus of claim 3, wherein the uplink channel quality informationincludes an estimated signal to noise plus interference ratio (SINR). 6.The apparatus of claim 1, wherein the determined downlink channelparameters include a number of data streams, a modulation/coding scheme,bit loading, or power loading for the data streams.
 7. The apparatus ofclaim 1, wherein the feedback information comprises a beamforming matrixor signal to noise plus interference ratio (SINR).
 8. The apparatus ofclaim 1, wherein the transmitter is further to transmit an instructionto the subscriber station to feedback the information only for thesubset of the estimated usable channels.
 9. The apparatus of claim 1,wherein the transmitter and the receiver are part of a transceiverhaving at least one common component, and the apparatus is a chipset.10. One or more non-transitory computer readable media comprisinginstructions configured to cause an eNB, upon execution of theinstructions by one or more processors of the base station, to: identifyone or more downlink channels of a number of downlink channels based onreceived uplink channel quality information of an uplink channel of theeNB; identify a subscriber station from a plurality of subscriberstations based on downlink parameters that are determined based on thereceived uplink channel quality information; transmit a signal to thesubscriber station identified using the downlink parameters; andreceive, from the subscriber station, an uplink message includingfeedback information related to the signal only for a subset of channelsof the number of downlink channels.
 11. The one or more non-transitorycomputer readable media of claim 10, wherein the uplink channel qualityinformation is based on channel quality of uplink spatial channelsand/or data streams.
 12. The one or more non-transitory computerreadable media of claim 11, wherein the uplink channel qualityinformation includes a mean or variance for one or more of the spatialchannels or data streams, or an estimated signal to noise plusinterference ratio (SINR).
 13. The one or more non-transitory computerreadable media of claim 10, wherein the downlink parameters include anumber of data streams, a modulation scheme, a coding scheme, or powerlevel of the data streams and are based on the estimated SINR.
 14. Theone or more non-transitory computer readable media of claim 13, whereinthe feedback information comprises a beamforming matrix or signal tonoise plus interference ratio (SINR).
 15. The one or more non-transitorycomputer readable media of claim 10, wherein the subset of channels is asubset of k relatively stronger channels of the number of downlinkchannels.
 16. A subscriber station comprising: an antenna; a processorcoupled to the antenna, the processor to: identify, based on a downlinksignal received on a downlink channel of a number of downlink channels,an indication from a base station to transmit an uplink message; andfacilitate, based on the indication, a transmission of an uplink messagethat includes feedback information corresponding to the downlink signal,wherein the feedback information is only for a subset of channels of thenumber of downlink channels, and wherein the number of the subset ofchannels is less than the number of downlink channels.
 17. Thesubscriber station of claim 16, wherein the subset of channels is asubset of relatively stronger channels of the number of downlinkchannels.
 18. The subscriber station of claim 16, wherein the processoris further to facilitate, prior to reception of the downlink signal,transmission of uplink channel quality information that is based onchannel quality of uplink spatial channels and/or data streams.
 19. Thesubscriber station of claim 18, wherein the uplink channel qualityinformation includes a mean or a variance of channel quality for each ofthe spatial channels and/or data streams, or the uplink channel qualityinformation includes an estimated signal to noise plus interferenceratio (SINR).
 20. The subscriber station of claim 16, further comprisinga display coupled with the processor.